Which of the following statements is true?

a. Gram-positive bacteria have a single cell wall anchored to the cell membrane by lipoteichoic acid.

b. Porins allow entry of substances into both Gram positive and Gram-negative bacteria.

c. The cell wall of Gram-negative bacteria is thick, and the cell wall of Gram-positive bacteria is thin.

d. Gram-negative bacteria have a cell wall made of peptidoglycan, whereas Gram-positive bacteria have a cell wall made of lipoteichoic acid.

In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.

Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation.

(a) Gram-positive bacteria have a single cell wall anchored to the cell membrane by lipoteichoic acid.

• In Gram-positive bacteria, lipoteichoic acid anchors the cell wall to the cell membrane. Gram-positive bacteria are bacteria that give a positive result in the Gram stain test

b. Porins allow entry of substances into both Gram positive and Gram-negative bacteria.

• Porins are pore proteins contained in the outer membrane of Gram-negative bacteria and they mediate the diffusion of small hydrophilic molecules.

c. The cell wall of Gram-negative bacteria is thick, and the cell wall of Gram-positive bacteria is thin.

• Gram-positive bacteria, the wall is thick, whereas in Gram-negative bacteria, the wall is thin. Hence the option (c) is not true.

d. Gram-negative bacteria have a cell wall made of peptidoglycan, whereas Gram-positive bacteria have a cell wall made of lipoteichoic acid.

• In Gram-negative bacteria, the cell wall is surrounded by an outer membrane that contains lipopolysaccharides and lipoproteins. Hence the option (d) is not true.